Zotero: The Tri-College Libraries recommend Zotero, a free online app that can format your bibliography, keep your citations organized, and even save your articles in the cloud so you can access them later from the library, home, or a café.
This handbook provides guidance on documenting sources and on writing style. This new edition includes instructions and examples for online publications and websites. See the print version for more detail on specific questions.
This page explains the system using separate bibliographic notes for citations rather than including them in the text as in often done in science papers. Examples are included for the different kinds of publications most often used by history students.
Chicago-Style Citation Quick Guide
Publication Manual of the American Psychological Association
The MLA's Handbook is a standard source for advice on formatting and documenting research in literature studies; it contains useful information on all matters pertaining to writing papers. This is the 2016 edition.